GB-A-1493620 describes a hydroisomerisation process to prepare base oils. The catalysts, which are known to be used in such a reaction generally, comprise a hydrogenation component and an acid component. GB-A-1493620 discloses a catalyst comprising nickel and tungsten as hydrogenation components, supported on an alumina carrier. The required acidity for the catalyst is provided by the presence of fluorine.
There have been many efforts to obtain a fluorine free hydroisomerisation catalyst. For example WO-A-9941337 describes a hydroisomerisation process wherein a slack-wax containing feed is contacted with a fluorine free catalyst. The disclosed catalyst consists of a platinum or palladium metal on a silica-alumina carrier. According to this publication a hydrotreatment step is preferably performed prior to the hydroisomerisation step in order to reduce the sulphur and nitrogen content to below 2 ppm, in order to avoid deactivation of the noble metal containing hydroisomerisation catalyst.
U.S. Pat. No. 5,370,788 describes a hydroisomerisation catalyst optionally containing fluorine. U.S. Pat. No. 5,370,788 describes a slack wax hydroisomerisation process wherein a non-fluorided nickel-molybdenum on silica-alumina carrier catalyst is used having almost only pores with diameters between 60-130 Å, a total surface area of 249 m2/g an a total pore volume of 0.5 cc/g, wherein the pore volume of the pores having a pore diameter of above 500 Å is 0.05 cc/g. The catalyst is said to be sulphur tolerant. The highest base oil yield on slack-wax reported in this publication is about 38 wt % obtained when the hydroisomerisation process was performed at about 70 bar and 370° C.
EP-A-537969 describes a hydroisomerisation catalyst optionally containing fluorine. A slack wax hydroisomerisation process is described wherein a nickel-molybdenum on silica-alumina carrier catalyst is used having almost only pores with diameters below 100 Å, a total surface area of between 100 and 250 m2/g. The catalyst is said to be sulphur tolerant. The high base oil yield on slack-wax are reported in this publication when the hydroisomerisation process was performed at about 70 bar and at temperatures about 400° C. According to this publication the products require a hydrofinishing step to improve their UV stability.
EP-A-666894 describes a hydroisomerisation catalyst containing no fluorine. A slack wax hydroisomerisation process is disclosed wherein a nickel-molybdenum on silica-alumina carrier catalyst is used having a certain macroporosity. The macroporosity is defined in that a considerable part of the pores have a diameter greater than 100 nm. The total pore volume is between 0.6 and 1.2 ml/g. The highest base oil yield on slack-wax reported in this publication is about 42 wt % obtained when the hydroisomerisation process was performed at 140 bar and at 391° C.
U.S. Pat. No. 5,292,989 describes a wax hydroisomerisation process wherein a catalyst is used comprising cobalt, nickel and molybdenum on a silica-alumina carrier wherein silica was deposited on the surface of the carrier. Slack wax is, according to the description, a possible feed. The sulphur and nitrogen content in the slack wax feed are preferably reduced to below 2 ppm before hydroisomerisation.